The present invention relates to a method according to the preamble of claim 1 for cleaning roll surfaces on a papermaking machine or the like, particularly the grooves, drilled perforations thereof and/or supported fabrics, and/or improving water drainage therein. The invention also relates to an apparatus according to the preamble of claim 8 suited for implementing the method.
In the art are known generally a plurality of different arrangements for cleaning roll surfaces and/or fabrics on a papermaking machine or equipment of a similar kind. For instance, an arrangement is known wherein the rolls of a papermaking machine, particularly its grooved-shell rolls, suction rolls, dryer rolls or other similar rolls, are cleaned by doctoring the rolls with the help of a doctor blade made from a polymer material, glass fiber, carbon fiber, steel or a combination thereof. This action serves by means of doctoring to clean the surface of a roll, particularly the grooves and/or perforations thereof and to remove water and dirt from the grooves and/or perforations and/or from the surface of the roll. The prior-art approaches are especially problematic in regard to the grooves and/or perforations of a roll when water and dirt must be removed therefrom. Particularly on the wire and press sections, water and/or dirt will adhere to the grooves and/or perforations of the rolls thus staying persistingly therein, which leads to inferior water drainage performance of the rolls/fabrics of a papermaking machine, reduced efficiency in the papermaking process, deteriorated quality of the web and a possible need to run the papermaking machine at a lower speed, whereby production loss is inevitable.
It is an object of the present invention to provide an entirely novel kind of arrangement for eliminating the reduction of operating efficiency in rolls and/or fabrics and for eliminating runnability problems on a paper/boardmaking machine or the like due to dirt plugging different kinds of roll surfaces and/or fabrics and by the effect of water and dirt adhering to the roll grooves and/or holes and/or fabrics. The goal of the invention is achieved by means of doctoring the surface of a roll with a novel type of doctoring apparatus, wherein pressurized gas, particularly compressed air, is used for generating to the incoming or outgoing side of a doctoring member such an overpressure or vacuum that enhances the water and dirt removal capabilities of the novel doctoring arrangement. The feed of the cleaning gas such as compressed air, is implemented using a purpose-designed gas ejection device suited for application of cleaning gas according to the invention to the surface of a roll and/or grooves and/or perforations of the roll surface. Additionally, the method and apparatus according to the invention can be used for cleaning, drying and removing water and dirt from the fabrics of a papermaking machine or the like machinery.
During its manufacture, the apparatus according to the invention can be provided with different kinds of integral sensors such as thermocouple wires and the like sensors suited for measuring the temperature and/or temperature profile of roll surfaces, for instance. Furthermore, it is possible to incorporate pressure, deflection, vibration or the like sensors that serve to monitor, e.g., the loading profile and/or possible leak-throughs under the doctoring elements, as well as moisture content, speed, acceleration and other sensors serving to monitor, e.g., the operational state of the doctoring element and/or roll and/or fabric.
More specifically, the invention is characterized by what is stated in the appended claims.
The arrangement according to the invention offers a number of significant benefits. The injection assembly of the cleaning gas such as compressed air can be used in a plurality of different applications. The apparatus is suited, e.g., for cleaning roll surfaces on a papermaking machine and removal of water and plugging materials from the grooves and/or perforations of roll surfaces. Additionally, the method and apparatus according to the invention is usable for cleaning, drying, water drainage and dirt removal on fabrics on a papermaking machine or the like.
Conventional cleaning or doctoring methods and apparatuses leave an excessively large amount of water and/or dirt on the surface and/or the grooves and/or perforations of a roll. This results in a reduced water drainage capacity and/or efficiency on the wire and press sections of a papermaking machine, problems in web runnability, web breaks and/or defects on the web. For instance, the grooves of grooved-shell rolls remain filled with a layer of water and/or dirt inasmuch a conventional doctor due to its linear shape and function cannot touch or clean but the outermost surface of roll. Conventional doctoring apparatuses and methods are also incapable of cleaning drilled holes of a perforated suction roll free from water and/or dirt due to the superficial contact of the scraping element with the roll surface alone. Today, separately mounted high-pressure water jets in cooperation with suction systems are being used for cleaning fabrics on a papermaking machine and the like systems. In these systems, the low efficiency of the cleaning equipment in regard to the high investment cost is a great disadvantage. Moreover, a fabric passed through such cleaning equipment still contains water and dirt, such as fiber and various surface sizes or fillers and adhesives.
The method and apparatus according to the invention intended for cleaning and/or doctoring of roll surfaces, particularly those of grooved-shell and/or suction rolls, on a papermaking machine achieve improved efficiency by virtue of an arrangement specifically developed for the implementation of the invention, in which arrangement pressurized gas, such as compressed air, is used for generating on the ingoing and/or outgoing side and/or interior space of a doctoring assembly according to the invention and/or between the doctor blades acting as the delineating walls of the doctoring assembly such a high pressure or a vacuum that serves to improve the water and dirt removal capabilities of the novel type of doctoring assembly. For instance, a first embodiment of the doctoring assembly intended for use on a grooved-shell roll is characterized in that the doctoring assembly is comprised of two doctor blades mounted in the same doctoring assembly complemented with a purpose-designed gas chamber such as a compressed-air chamber. The interblade space forms a closed and tightly delineated pocket whereto gas, particularly compressed air, can be passed from the compressed-air chamber of the doctoring assembly in a purpose-designed and controlled manner via openings, nozzles and/or slits made according to the invention to the wall of the chamber in a purpose-designed and controlled manner. Consequently, into the pocket between doctor blades of the doctoring assembly can be formed by the introduced gas, particularly compressed air, a high pressure that tends to escape outward via the grooves of the grooved-shell roll from under the first doctor blade of the doctoring assembly to the front side, that is, the incoming side of the doctoring assembly. The pressurized gas or compressed air thus escaping from under the doctor blade via the grooves of the grooved-shell rolls forms in front of and under the doctor blade and into the grooves a high-pressure barrier zone that prevents water and/or dirt adhering to the roll grooves from passing with rotation of roll via and from under the doctor blade. A portion of the pressurized gas pumped into the interblade pocket, such as compressed air,tends to escape via the cleaned grooves of the grooved-shell roll from under the second doctor blade to the rear side, later called the outgoing side, of the doctoring assembly. The pressurized gas such as compressed air escaping from under the doctor blade, via the grooves of a grooved-shell roll, generates on the outgoing side of the doctoring assembly and particularly, under the doctor blade thereof, a high vacuum that works by way of an ejector effect so as to remove the possible remains of water and dirt still adhering to the grooves.
A second embodiment of the doctoring assembly intended for use on a suction roll is characterized in that the doctoring assembly is comprised of two doctor blades mounted in the same doctoring assembly complemented with a purpose-designed gas chamber such as a compressed-air chamber. The interblade space forms a closed and tightly delineated pocket into which gas, particularly compressed air, can be passed from the compressed-air chamber of the doctoring assembly in a purpose-designed and controlled manner via openings, nozzles and/or slits made to the wall of the chamber in a purpose-designed and controlled manner according to the invention. Consequently, into the pocket between doctor blades of the doctoring assembly can be formed by the introduced gas, particularly compressed air, a high pressure that tends to escape outward to the outgoing side of the doctoring assembly via openings, nozzles and/or slits that are made to the second doctor blade on the rear side the chamber in a purpose-designed and controlled manner. The pressurized gas such as compressed air thus escaping through said second, latter doctor blade forms behind and under the doctor blade a high-pressure barrier zone that works by way of an ejector effect so as to remove the possible remains of water and dirt still adhering to the perforations of the roll shell. In perforated suction rolls also having grooved shell, the above-described features of the doctoring assemblies may obviously be used in a combined manner.
Suction rolls, grooved-shell rolls and the like are today cleaned using a so-called foil formed by a thick strip of an elastomeric material. Now, a foil can be replaced by a doctoring assembly according to the invention, the doctoring assembly including an integral chamber for pressurized gas such as compressed air, whereby the cleaning gas such as compressed air is passed from the chamber via openings, nozzles and/or slits, which are made according to the invention in a purpose-designed manner to the wall of the compressed-air chamber of the doctoring assembly, in a controlled manner to the incoming or front side and/or to the outgoing side of the doctor element of the assembly or also therebehind and thereunder.
Respectively, the fabrics of a papermaking machine or the like are today cleaned by separately mounted high-pressure shower systems in combination with suction systems. Such conventional arrangements may be replaced by a doctoring assembly according to the invention, the doctoring assembly including an integral chamber for pressurized gas such as compressed air, whereby the gas such as compressed air is passed via openings, nozzles and/or slits, which are made in a purpose-designed manner to the wall of the compressed-air chamber of the doctoring assembly, in a controlled manner to the incoming or front side and/or to the outgoing side of the doctoring assembly or also therebehind and thereunder. The doctoring assembly is located to operate in a close proximity to the fabric of a papermaking machine or the like machinery.
The doctoring assembly according to the invention that is above described by way of exemplifying embodiments is capable of reducing the amount of water and/or dirt carried over in the grooves and/or perforations made on the rolls of the wire and press sections, thus offering improvement in the water removal properties of rolls and fabrics on a papermaking machine, a higher solids content of the produced web, enhanced efficiency in papermaking, higher quality of paper web and a possibility of increasing the speed of the papermaking machine, whereby all these factors in combination provide higher overall efficiency of production.
The doctoring assembly according to the invention described above by way of exemplifying embodiments can also be utilized to control the air pressure differences, air flows and similar factors at a close proximity to the surfaces of rolls, particularly those of the dryer cylinders, that affect web behavior.
Improved water drainage efficiency on a papermaking machine elevates the solids content of the web after the wire and press sections. The solids content of the web particularly after the press section has a tremendous economic impact inasmuch the amount of steam required for drying the web forms one of the major singular cost factors in papermnaking.
The doctoring assembly according to the invention can be further utilized to affect the properties of rolls, fabrics and/or the paper web, such as the uniformity of moisture and temperature profiles of the roll surfaces, fabrics and/or the paper web, and to reduce spot adhesion of the paper web to the fabrics at the outgoing side of the press.
Furthermore, the doctoring assembly according to the invention can be provided during its manufacture with different kinds of integral sensors such as thermo-couple wires and the like sensors suited for measuring the temperature and/or temperature profile of roll surfaces. It is also possible to incorporate pressure, deflection, vibration or the like sensors that serve to monitor, e.g., the loading profile and/or possible leak-throughs under the doctoring elements, as well as moisture content, speed, acceleration and other sensors serving to monitor, e.g., the operational state of the doctoring element. Such sensors integrated into the doctoring assembly according to the invention can be used for monitoring the properties of the doctoring elements, rolls, fabrics andlor the paper web, such as the moisture content, temperature, moisture and/or temperature profiles, the contact of the doctoring element with the roll and/or fabric surfaces, and the like parameters.
In addition to the functions described above, the doctoring assembly according to the invention can be used for cleaning, drying and unplugging the fabrics of a papermaking machine or the like machinery from water and dirt by way of using the assembly in the same fashion as a water foil.